This invention relates to contact structures, and more particularly to contact structures used in the fabrication of integrated circuits.
An integrated circuit, such as a dynamic random access memory (DRAM) includes passive devices, such as capacitors, and active devices, such as metal-oxide semiconductor field-effect transistors (MOSFETS), fabricated on a single substrate. In fabricating an integrated circuit to perform a particular function, the passive and active devices are coupled together. For example, a capacitor electrode is electrically coupled to a MOSFET drain or source to form a dynamic random access memory (DRAM) cell for storing information.
One method of coupling a capacitor electrode to a MOSFET drain or source includes the operation of directly coupling the capacitor electrode to the drain or source by fabricating the capacitor electrode at the drain or source. Unfortunately, several problems arise when a non-silicon electrode is directly coupled to a MOSFET drain or source. First, the electrode can experience oxidation, which interferes with the electrode conductivity and may cause unpredictable memory cell operation. Electrode oxidation is most likely to occur during capacitor formation processes performed in an O2 atmosphere. Second, atomic migration to and from a substrate, such as silicon substrate, may occur between the substrate in which the MOSFET source and drain are formed and other integrated circuit elements, such as the dielectric layer of a capacitor. Atomic migration alters the electrical properties of the integrated circuit elements and may cause unpredictable memory cell operation.
One solution to these problems is to form a contact structure having a barrier layer located between the electrode and the source or drain for blocking oxygen migration and atomic migration to and from the substrate. Unfortunately, a single barrier layer that effectively blocks both oxygen migration and atomic migration from the substrate may react with the conductive layer fabricated at the source or drain and cause unpredictable circuit operation.
For these and other reasons, there is a need for the present invention.
The above mentioned problems with coupling devices in integrated circuits and other problems are addressed by the present invention and will be understood by reading and studying the following specification. A contact structure is described that includes one or more layers and other structures for blocking atomic migration in an integrated circuit, which improves the reliability of the circuit.
The present invention provides, in one embodiment, a contact including a polysilicon layer formed on a substrate, one or more barrier layers formed above the polysilicon layer, and a barrier structure encircling the polysilicon layer and the one or more barrier layers. The polysilicon layer provides a conductive material for coupling to an active or a passive device in an integrated circuit. At least one of the one or more barrier layers restricts the migration of atoms to and from the substrate, and at least one of the one or more barrier layers restricts the migration of oxygen atoms. Restricting the migration of substrate atoms, prevents the electrical properties of the integrated circuit devices from being inadvertently altered during circuit fabrication. Restricting the migration of oxygen atoms, deters oxidation at electrode surfaces, such as capacitor electrode surfaces. Since the barrier layers of the contact are also electrically conductive, the contact is suitable for use in interconnecting integrated circuit devices.
In an alternate embodiment, the present invention provides a method of fabricating a contact. The method includes forming a polysilicon layer and a tungsten nitride layer above a base integrated circuit structure. The polysilicon layer is formed at an electrical connection site of an integrated circuit device. The polysilicon layer and the tungsten nitride layer are etched to a level below the surface of the base integrated circuit structure. The polysilicon layer encircling the contact is etched much deeper, and a silicon nitride layer is formed to encircle the tungsten nitride layer. A ruthenium silicide layer is formed above the tungsten nitride layer as an oxygen barrier. The silicon nitride layer prevents the polysilicon layer from reacting with the ruthenium silicide layer. After polishing and cleaning, the ruthenium silicide layer is ready for coupling to an integrated circuit device.